This article will give an in-depth view at electric switches.
The article will discuss topics such as:
This chapter will explore the concept of electric switches, including their types and operational mechanisms.
An electric switch is an electromechanical device designed to open or close an electrical circuit. By doing so, it controls the flow of electric current, either interrupting it or allowing it to pass through.
Switches are designed to interrupt or control the flow of electric current, essentially manipulating the movement of electrons through a circuit.
The concept behind a switch is rooted in the basic principles of electricity and the use of conductive materials to facilitate current flow. A switch creates a break or discontinuity in the conductor, stopping the current when the circuit is opened. This principle dates back to the early days of electrical engineering and the creation of the first circuits.
Essentially, a switch introduces an air gap into the circuit. This air gap has different electrical characteristics compared to the conductive materials, and when it's sufficiently large, it prevents the current from flowing. The primary function of a switch is to modify the electrical properties within a circuit to control electron flow. However, not all switches operate through physical movement; some use other methods to achieve the same effect.
Switches offer a way to manage the flow of electrical current to various loads. A key feature of a switch is its ability to either allow or interrupt the current flow based on the operator's needs.
Many electric switches operate by creating an air gap between two contacts to break the circuit. The contacts need to be separated quickly enough to ensure proper operation.
In most electronic switches, the circuit's state is altered by changing the resistance of the connection. This resistance can be increased to create an open circuit or decreased to close the circuit. Often, these switches do not have any physically moving parts.
Another crucial factor is how the switch responds to its actuator. The actuator, which can be either automatic or manual, is responsible for making or breaking the circuit. Its role is to initiate a change in the connection's state. Actuators may involve physical components such as levers or slides, or they may react to other events like overvoltage or changes in light intensity.
If the equipment connected through the switch requires protection, a fuse is often included as part of the switch assembly.
This chapter will cover the various ratings and categories associated with electric switches.
When selecting and using electric switches, it is essential to consider their ratings. These ratings include:
Current Rating - the maximum electric current that the switch is designed to carry. The switch might start incurring physical damage when this limit is exceeded. Such damage includes overheating, deformation, and melting of some of the components of that switch.
For a circuit breaker, the rating is the current above which the breaker "trips". Tripping, in this context, means breaking up the circuit. There is often an allowance from the rated current before the breaker trips. This allowance is often expressed as a percentage of the rated current.
For some electronic switches, the current rating may show the value above which the actuator can no longer switch the connection off. Alternatively, it is the maximum current that the switch is designed to handle.
Voltage Rating - the maximum voltage that the switch is designed to withstand. Higher voltages cause more sparks than desirable.
For some electronic switches, such as the thyristor, the voltage rating is the maximum voltage the switch can block. Any higher voltage will switch the thyristor on without the intended actuation. The intended actuation is often the presence of a gate voltage.
An electrical switch can have different ratings depending on whether it's used in AC or DC circuits.
AC Circuits: In alternating current (AC) circuits, the current fluctuates, causing the voltage to periodically drop to zero twice every cycle. This behavior creates moments when the electric field is zero, which helps to extinguish arcing when the circuit is broken.
DC Circuits: Direct current (DC) circuits have a steady, unidirectional current, which can lead to more prolonged arcing. This necessitates faster switching speeds to manage the connection's opening and closing. Consequently, the maximum voltage rating for DC is typically lower than that for AC for the same switch.
Electric switches can be classified into several categories. The primary categories are outlined below.
Momentary switches are characterized by maintaining one state until they are energized, at which point they switch to the alternate state. Once de-energized, they revert to their original state. An early example of momentary switches includes those used in telegraph machines. Momentary switches typically come in two forms:
This type of switch remains in its current state until it is energized to change to the alternate state. Common examples include domestic light switches and car ignition switches, which traditionally operate using this mechanism.
The previously discussed types of switches can be categorized further based on their specific designs, which are detailed below.
This switch is named for its layout – it is housed in a dual inline package (DIP).
Electrical switches are used to connect electrical circuits. They differ from electronic switches, which use electrical signals to control operations and make decisions.
These switches are equipped with a mechanism to disconnect the circuit in the event of an overload. Circuit breakers that respond to current surges are more commonly used than those that react to voltage surges.
The actuator in a breaker includes a recoil mechanism, like a spring, and has an additional system to hold the switch in place once it is reset. During operation, the spring mechanism breaks the circuit when the switch’s holding mechanism is deactivated, which happens when a surge triggers a third mechanism.
These switches incorporate a fuse into a standard switch setup to protect the load when no other protection is available.
This switch monitors the difference between the current supplied to the load and the current returning from it. If a discrepancy is detected, indicating a current leak, the switch will cut off the current to the load.
These switches consist solely of an actuator and electrical contacts, lacking any built-in protection. Often, protective features are included in the circuit systems where these switches are used.
These switches are designed to either connect electronic circuits or use electronic signals to establish connections in electrical circuits. Electronic switches rely on specific current and/or voltage signals, which serve as inputs or outputs, to control actions within the circuit.
Typically, the actuation of these switches involves applying an electrical current to a "gate," which is generally much smaller than the current it is intended to manage. This gate usually receives a direct current, while the controlled current can be either alternating current (AC) or direct current (DC).
These switches are designed to connect just one circuit at a time.
These switches enable the simultaneous operation of several circuits.
Double Pole Double Throw - These have two inputs and four outputs. They are like two single pole double throw switches being operated by the same actuator.
Although technically possible, this arrangement is not typical. It is usually substituted by a series of parallel switches, like the standard branches, where each branch is equipped with its own switch and outlet.
Using one switch with a single input and multiple outlets presents drawbacks, such as a common failure point and reduced ability to isolate individual outlets.
This setup involves a group of switches mounted on a single panel. Commonly used in both residential and commercial settings, these panels typically manage related circuits and may include multiway switching options.
This refers to a collection of switches, fuses, and similar devices. While the fundamental concept is similar to that of a switch, the term "switchgear" specifically pertains to high voltage systems, including power generation and distribution. Due to the unique properties of high-voltage electricity, switchgear includes specialized features not typically found in standard household switches.
Switchgear is frequently installed outdoors and can be controlled either manually or remotely. Managing the diffusion of arcing during circuit interruption is crucial for its operation. Due to the high voltages involved, significant care is needed to handle arcing. Switchgear breakers utilize different types of insulation media, such as:
These switches are designed for outdoor use and, in some cases, underwater applications. Their casings are sealed to prevent water from coming into contact with the electrical components.
This chapter will discuss the design of electric switches.
Relays are electrical devices utilized to control a circuit with a separate power signal, typically of low power. In essence, a relay functions as an electrically-operated switch.
Traditional relay switches rely on an electromagnetic coil. When an electrical signal energizes the coil, it attracts a metal contact arranged in a specific configuration. This movement of the metal contact either makes or breaks a connection. A mechanism typically returns the contact to its original position once the coil is de-energized. The metal contact remains in its attracted state as long as the coil is energized, making the relay function similarly to a momentary switch.
A latching relay differs from the traditional relay by functioning more like a maintained switch. It usually requires signals of opposite polarity to toggle the circuit open and closed. The absence of power does not affect the relay's state, meaning it retains its position regardless of power supply. Latching relays are used in applications where a circuit needs to remain in one state for extended periods without continuous power to the coil.
In electrical power systems, relays are employed to operate circuit breakers. Electromagnetic relays were also widely used in telecommunication systems for analog switching until recent advancements. They are also used in railway signaling and transceiver switching.
Solid-state relays represent the electronic counterpart to electromagnetic relays, utilizing semiconductor components to control isolated circuits. An example is an optocoupler, which combines a light-emitting diode (LED) with a photodiode to perform this function.
Actuator mechanisms on a switch enable manual control of a circuit's on and off states. Examples of such actuator mechanisms include:
These switches come in the form of a button or a similar key. They can either be a maintained or momentary switch. The push button is the most common type of momentary switch. A normally closed push button switch is often called the push to break, and a normally open push button switch is often called the push to make a switch. The maintained push button switch is attached to a mechanism that alternately holds and releases with consecutive pushes.
Push buttons are generally configured as two-state switches. Although push buttons with more than two states can be designed, this setup is relatively uncommon.
Rocker switches are named for their rocking motion. They consist of two main components: a movable part that rocks back and forth and a fixed part that remains stationary. The switch toggles between two extreme positions, typically marked as ‘on’ and ‘off’. Rocker switches are widely used for wall-mounted applications, especially in residential settings. They can also be mounted directly on devices to control power, though in such cases, they often compete with maintained push button switches.
The rocking action means that pressing one end of the switch causes the opposite end to move in the opposite direction. This movement is achieved by pressing the desired end of the switch. The rocking mechanism is connected to a contact, so rocking the switch in one direction completes a circuit, while rocking it in the opposite direction breaks the circuit.
Rotary switches are typically used in applications requiring more than two states, beyond the simple on and off functions. The term ‘rotary’ describes the method of selecting states, rather than indicating a specific number of states. For applications with only two states, rocker and push button switches are more commonly used.
A rotary switch operates by turning a knob or similar component around an axis, which moves a contact through a circular array of connectors. This action alternates connections between different states. The rotation can be either smooth or stepped, and the switch may have a fixed number of states or an ‘off’ position combined with a continuously variable ‘on’ setting. Rotary switches are usually maintained switches and can be installed on walls for industrial use or directly on devices such as electric ovens.
Another common example of a rotary switch is the traditional key and socket car ignition switch.
This type of switch utilizes a lever to alter the state of a connection. It can function as either a momentary or maintained switch and is typically designed as a two-state switch. Toggle switches are commonly used for household circuit breakers and are known for their relatively high switching speeds compared to other types of electrical switches.
This switch operates by sliding a control from one position to another, thereby shifting a contact and altering the connection states. Although it is commonly a two-state switch, it can also be designed to accommodate multiple states. While it serves as a practical alternative to rotary switches, the latter is generally favored for most multi-state applications.
The slider's movement can be either smooth or stepped.
A contactor is a key component in an electrical circuit, functioning primarily as a switch. It controls the flow of electrical power and signals by making or breaking contact. When the contactors are engaged, the circuit is closed, allowing current to flow; when they are disengaged, the circuit is open and current is interrupted.
Contactors are typically constructed from metals, but any conductive material can be utilized in their manufacture.
The following materials are commonly employed in the production of contactors:
Copper is a very good conductor of electricity (and heat), with its conductivity being behind only that of silver. A common copper alloy used in the making of contactors is brass.
Silver is one of the best conductors of electricity and is known for its excellent oxidation resistance, along with its alloys.
Gold is a good conductor, ranking just behind copper and silver in conductivity. It also has high corrosion resistance. However, gold contactors are relatively rare due to the cost and availability of gold.
Platinum is among the most costly materials used in electronics. The high cost is even more significant when considering that volume often outweighs weight, and platinum has a notably high specific weight.
The electrical resistance of a material can be influenced by the dimensions of the conductors, not solely by weight. While there might be a correlation between weight and resistance, they are not directly dependent on each other.
Carbon, though a non-metal, can conduct electricity in certain forms. It is less effective compared to metals and is typically used for experimental and specialized industrial purposes.
Many metals can conduct electricity and find use in various applications where resistance is not a primary concern.
These metals are:
This chapter will cover the properties of contactors in switches and the management of heat in switch operations.
When selecting and applying electrical switches, it is important to consider various contactor properties. These include:
This is a crucial characteristic of the contactor. Low resistance helps minimize heating in the contactors and, consequently, in the switch itself.
During their service lives, contacts might be exposed to high humidity and/or elevated temperatures. To maintain their electrical and mechanical properties, they must be resistant to corrosion.
This refers to a component's resistance to material loss caused by mechanical action. In many switch designs, the contacts slide against each other as they engage and disengage circuits. This sliding action generates friction and abrasion, which contribute to wear. Resistance to this wear is essential for the longevity of both the contactors and the switch.
Electronic switches often require temperature control because their performance can be influenced by temperature variations.
Typically, an electronic switch's rating is specified for a particular temperature range.
Temperature can be managed by attaching a heat sink to the switch. A heat sink is generally made of a metal with high thermal conductivity and emissivity, which helps the switch dissipate heat more efficiently than it would on its own.
Another method is to place the switch in an air-conditioned environment, which helps ensure it operates within its optimal performance range.
This chapter will cover deformation, malfunctions, and hazards associated with switches.
The operation of a switch relies on its ability to repeatedly move between several predefined physical positions and maintain this functionality over an extended lifespan. This process may involve deforming the contactor, which must return to specific positions under predefined mechanical loads applied by actuators. Such deformation often involves bending, which requires some degree of springiness in the contactor. Alternatively, the contactor may be made rigid and coupled with a spring or multiple springs.
Contactors are typically electrically isolated from the ground and users, which means they are housed in non-conductive materials, usually plastic. While most switch housings are made of plastic, metal may be used for certain applications, such as circuit breakers. Regardless of the material, the housing and actuator mechanism are always electrically separated from the contacts. The switch's ratings are determined by adjusting the contactor characteristics and the overall design of the switch.
Electric switches can experience various malfunctions. Recognizing these potential issues is crucial for effective troubleshooting. Examples of such malfunctions include when the switch:
This issue occurs when a contactor is damaged, deformed, or melted, preventing it from closing the connection as intended by the actuator. For most switches, the solution is to replace the entire switch. In the case of fused switches, failure to close the circuit may lead to a blown fuse, which can be fixed by replacing the fuse.
A switch might fail to turn off due to deformation of the contactors, which can prevent the actuator from controlling the contactor correctly. Alternatively, if the mechanism connecting the actuator to the contactors is damaged, it may result in loose or ineffective actuator movement.
In some electronic switches, excessive currents can lead to a failure to break the circuit, causing the switch to become latched in the 'on' position.
This occurs when either the actuator or the contactor becomes deformed, preventing the contactors from separating properly as intended by the actuator's input. As a result, the switch's rating is compromised, leading to failure before the switch reaches its rated parameters.
A circuit breaker may fail to trip during an overload due to wear or manufacturing defects, which can prevent it from detecting an increase in current. This can result in the breaker allowing excessive current to pass through or failing to trip altogether. In either scenario, the breaker must be replaced.
This issue occurs when current leaks to the ground or when there is a short circuit in an appliance's wiring. If exposed wiring comes into contact with a conductive part of the appliance unintentionally, it can create an alternative path to ground. If this short circuit occurs before the electrical load, it can cause a surge that might trip a breaker or blow a fuse.
This occurs when there is an opening between contacts and a sufficiently high electric field that ionizes the air, allowing current to arc across the gap. This arcing manifests as a spark, similar to the phenomenon of lightning. Reducing the air gap, increasing the voltage, or both will intensify the electric field, making sparks more noticeable during overloads or in switches that can no longer maintain a sufficiently large gap.
A switch can overheat if:
A short circuit happens when current takes an unintended path, typically due to insulation failure in some part of the circuit. One of the functions of a switch is to respond to certain types of short circuits.
Electric switches, like all equipment and tools, are susceptible to various hazards. The most common hazards include:
Fire hazards can arise from excessive sparking or a switch's failure to react appropriately to issues in the power circuit, such as surges or leaks. They may also occur if a switch is used beyond its rated capacity, potentially causing it to explode under certain conditions.
Surge damage occurs when a switch allows surges to pass through to the connected equipment. This is most common with basic switches lacking protective mechanisms. It can also happen if the switch's ratings are mismatched with the equipment's requirements, such as when it fails to cut off power as needed or allows excess power to pass through.
This malfunction can also lead to electrocution, which happens if the switch fails to respond to short circuits or leakage currents.
Switches have evolved and diversified considerably since their invention. They also continue to fit into cross-cutting issues affecting the globe, including environmental sustainability and automation. In as much as it may not be far-fetched to expect switches to change form considerably in the distant future, the underlying principles are likely to remain salient, and the current value chains may continue to stand a good chance to keep improving.
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